/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package com.boost.bio.line;


import java.io.IOException;
import java.io.Reader;
import java.io.UncheckedIOException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

/**
 * Reads text from a character-input stream, buffering characters so as to
 * provide for the efficient reading of characters, arrays, and lines.
 *
 * <p> The buffer size may be specified, or the default size may be used.  The
 * default is large enough for most purposes.
 *
 * <p> In general, each read request made of a Reader causes a corresponding
 * read request to be made of the underlying character or byte stream.  It is
 * therefore advisable to wrap a BufferedReader around any Reader whose read()
 * operations may be costly, such as FileReaders and InputStreamReaders.  For
 * example,
 *
 * <pre>
 * BufferedReader in
 *   = new BufferedReader(new FileReader("foo.in"));
 * </pre>
 * <p>
 * will buffer the input from the specified file.  Without buffering, each
 * invocation of read() or readLine() could cause bytes to be read from the
 * file, converted into characters, and then returned, which can be very
 * inefficient.
 *
 * <p> Programs that use DataInputStreams for textual input can be localized by
 * replacing each DataInputStream with an appropriate BufferedReader.
 *
 * @author Mark Reinhold
 * @see java.nio.file.Files#newBufferedReader
 * @since JDK1.1
 */

public class CharSplitBufferedReader extends Reader {


    private char split;

    //底层绑定的字符输入流
    private Reader in;
    //内部充当缓冲区的字符数组
    private char cb[];
    //缓冲区当前的有效字符数
    private int nChars;
    //缓冲区下一次字符读取的位置
    private int nextChar;
    //标识标记无效。设置了标记，但是被标记位置由于某种原因导致标记无效
    private static final int INVALIDATED = -2;
    //标记位置初始化位置
    private static final int UNMARKED = -1;
    //标记位置，初始化位置-1标识未标记
    private int markedChar = UNMARKED;
    /**
     * 在仍保留该标记的情况下，对可读字符数量的限制。在读取达到或者超过此限制的字符之后尝试重置输入流可能会失败。
     * 限制值大于缓冲区大小时会导致分配一个新的缓冲区，新缓冲区的容量不小于该值，因此应该小心分配该值
     */
    private int readAheadLimit = 0; /* Valid only when markedChar > 0 */

    /**
     * If the next character is a line feed, skip it
     * 标识是否跳过换行符
     */
    private boolean skipLF = false;

    /**
     * The skipLF flag when the mark was set
     * 表示当做了标记之后，是否忽略换行符
     */
    private boolean markedSkipLF = false;
    //字符缓冲区的默认大小
    private static int defaultCharBufferSize = 8192;
    //每行默认的字符个数
    private static int defaultExpectedLineLength = 80;

    /**
     * Creates a buffering character-input stream that uses an input buffer of
     * the specified size.
     *
     * @param in A Reader
     * @param sz Input-buffer size
     * @throws IllegalArgumentException If {@code sz <= 0}
     */
    public CharSplitBufferedReader(Reader in, int sz) {
        super(in);
        if (sz <= 0)
            throw new IllegalArgumentException("Buffer size <= 0");
        this.in = in;
        cb = new char[sz];
        nextChar = nChars = 0;
        split='\u001F';
    }

    /**
     * Creates a buffering character-input stream that uses a default-sized
     * input buffer.
     *
     * @param in A Reader
     */
    public CharSplitBufferedReader(Reader in,char split) {
        this(in, defaultCharBufferSize);
        this.split=split;
    }

    /**
     * Checks to make sure that the stream has not been closed
     */
    private void ensureOpen() throws IOException {
        if (in == null)
            throw new IOException("Stream closed");
    }

    /**
     * Fills the input buffer, taking the mark into account if it is valid.
     */
    private void fill() throws IOException {
        int dst;
        //未标记，则从缓冲区数组索引位置0处开始填充数据
        if (markedChar <= UNMARKED) {
            /* No mark */
            dst = 0;
        } else {
            /* Marked 计算当前读取位置到标记位置之间的距离*/
            int delta = nextChar - markedChar;
            //如果距离超出readAheadLimit，标记无效
            if (delta >= readAheadLimit) {
                /* Gone past read-ahead limit: Invalidate mark */
                markedChar = INVALIDATED;
                readAheadLimit = 0;
                //缓冲区数组起始填充位置为0
                dst = 0;
            } else {
                //如果readAheadLimit小于缓冲区数组长度
                if (readAheadLimit <= cb.length) {
                    /* Shuffle in the current buffer */
                    System.arraycopy(cb, markedChar, cb, 0, delta);
                    markedChar = 0;
                    dst = delta;
                } else {
                    /* Reallocate buffer to accommodate read-ahead limit */
                    char ncb[] = new char[readAheadLimit];
                    System.arraycopy(cb, markedChar, ncb, 0, delta);
                    cb = ncb;
                    markedChar = 0;
                    dst = delta;
                }
                nextChar = nChars = delta;
            }
        }

        int n;
        do {
            //底层字符输出流尝试读取一段字符数据填满缓冲区数组
            n = in.read(cb, dst, cb.length - dst);
        } while (n == 0);
        //读取字符个数大于0，更新缓冲区字符个数nChars
        if (n > 0) {
            nChars = dst + n;
            nextChar = dst;
        }
    }

    /**
     * 读取单个字符，当到达流末尾的时候返回-1
     * Reads a single character.
     *
     * @return The character read, as an integer in the range
     * 0 to 65535 (<tt>0x00-0xffff</tt>), or -1 if the
     * end of the stream has been reached
     * @throws IOException If an I/O error occurs
     */
    public int read() throws IOException {
        synchronized (lock) {
            //检测流状态，若底层输入流in为null则说明流已经关闭抛出IO异常
            ensureOpen();
            for (; ; ) {
                //如果缓冲区数据已被读取完，则从底层字符输入流读入数据填充到缓冲区，如果填充完缓冲区状态仍未被重置则
                //证明已达到流末尾返回-1
                if (nextChar >= nChars) {
                    fill();
                    if (nextChar >= nChars)
                        return -1;
                }
                //若设置跳过换行符
                if (skipLF) {
                    //先设置skip为false
                    skipLF = false;
                    //若当前读取到字符为换行符，跳过继续读取下一个字符
                    if (cb[nextChar] == split) {
                        nextChar++;
                        continue;
                    }
                }
                //返回从缓冲区读取到的字符
                return cb[nextChar++];
            }
        }
    }

    /**
     * Reads characters into a portion of an array, reading from the underlying
     * stream if necessary.
     */
    private int read1(char[] cbuf, int off, int len) throws IOException {
        if (nextChar >= nChars) {
            /* If the requested length is at least as large as the buffer, and
               if there is no mark/reset activity, and if line feeds are not
               being skipped, do not bother to copy the characters into the
               local buffer.  In this way buffered streams will cascade
               harmlessly. */
            if (len >= cb.length && markedChar <= UNMARKED && !skipLF) {
                return in.read(cbuf, off, len);
            }
            fill();
        }
        if (nextChar >= nChars) return -1;
        if (skipLF) {
            skipLF = false;
            if (cb[nextChar] == split) {
                nextChar++;
                if (nextChar >= nChars)
                    fill();
                if (nextChar >= nChars)
                    return -1;
            }
        }
        int n = Math.min(len, nChars - nextChar);
        System.arraycopy(cb, nextChar, cbuf, off, n);
        nextChar += n;
        return n;
    }

    /**
     * Reads characters into a portion of an array.
     *
     * <p> This method implements the general contract of the corresponding
     * <code>{@link Reader#read(char[], int, int) read}</code> method of the
     * <code>{@link Reader}</code> class.  As an additional convenience, it
     * attempts to read as many characters as possible by repeatedly invoking
     * the <code>read</code> method of the underlying stream.  This iterated
     * <code>read</code> continues until one of the following conditions becomes
     * true: <ul>
     *
     * <li> The specified number of characters have been read,
     *
     * <li> The <code>read</code> method of the underlying stream returns
     * <code>-1</code>, indicating end-of-file, or
     *
     * <li> The <code>ready</code> method of the underlying stream
     * returns <code>false</code>, indicating that further input requests
     * would block.
     *
     * </ul> If the first <code>read</code> on the underlying stream returns
     * <code>-1</code> to indicate end-of-file then this method returns
     * <code>-1</code>.  Otherwise this method returns the number of characters
     * actually read.
     *
     * <p> Subclasses of this class are encouraged, but not required, to
     * attempt to read as many characters as possible in the same fashion.
     *
     * <p> Ordinarily this method takes characters from this stream's character
     * buffer, filling it from the underlying stream as necessary.  If,
     * however, the buffer is empty, the mark is not valid, and the requested
     * length is at least as large as the buffer, then this method will read
     * characters directly from the underlying stream into the given array.
     * Thus redundant <code>BufferedReader</code>s will not copy data
     * unnecessarily.
     *
     * @param cbuf Destination buffer
     * @param off  Offset at which to start storing characters
     * @param len  Maximum number of characters to read
     * @return The number of characters read, or -1 if the end of the
     * stream has been reached
     * @throws IOException If an I/O error occurs
     */
    public int read(char cbuf[], int off, int len) throws IOException {
        synchronized (lock) {
            ensureOpen();
            if ((off < 0) || (off > cbuf.length) || (len < 0) ||
                    ((off + len) > cbuf.length) || ((off + len) < 0)) {
                throw new IndexOutOfBoundsException();
            } else if (len == 0) {
                return 0;
            }

            int n = read1(cbuf, off, len);
            if (n <= 0) return n;
            while ((n < len) && in.ready()) {
                int n1 = read1(cbuf, off + n, len - n);
                if (n1 <= 0) break;
                n += n1;
            }
            return n;
        }
    }

    /**
     * Reads a line of text.  A line is considered to be terminated by any one
     * of a line feed ('\n'), a carriage return ('\r'), or a carriage return
     * followed immediately by a linefeed.
     *
     * @param ignoreLF If true, the next '\n' will be skipped
     * @return A String containing the contents of the line, not including
     * any line-termination characters, or null if the end of the
     * stream has been reached
     * @throws IOException If an I/O error occurs
     * @see java.io.LineNumberReader#readLine()
     */
    String readLine(boolean ignoreLF) throws IOException {
        StringBuffer s = null;
        int startChar;

        synchronized (lock) {
            ensureOpen();
            //是否跳过换行符
            boolean omitLF = ignoreLF || skipLF;
            for (; ; ) {
                //缓冲区字符数据已经读完则调用fill方法填充字符数据
                if (nextChar >= nChars)
                    fill();
                //已到达流末尾，直接返回已读取字符串
                if (nextChar >= nChars) { /* EOF */
                    if (s != null && s.length() > 0)
                        return s.toString();
                    else
                        return null;
                }
                boolean eol = false;
                char c = 0;
                int i;

                /* Skip a leftover split, if necessary 若设置跳过换行符omitLF，则跳过*/
                if (omitLF && (cb[nextChar] == split))
                    nextChar++;
                skipLF = false;
                omitLF = false;

                charLoop:
                for (i = nextChar; i < nChars; i++) {
                    c = cb[i];
                    //碰到行终止符或者回车符则跳出循环
                    if (c == split) {
                        eol = true;
                        break charLoop;
                    }
                }

                startChar = nextChar;
                nextChar = i;

                if (eol) {
                    String str;
                    if (s == null) {
                        str = new String(cb, startChar, i - startChar);
                    } else {
                        s.append(cb, startChar, i - startChar);
                        str = s.toString();
                    }
                    nextChar++;
                    if (c == split) {
                        skipLF = true;
                    }
                    return str;
                }

                if (s == null)
                    s = new StringBuffer(defaultExpectedLineLength);
                s.append(cb, startChar, i - startChar);
            }
        }
    }

    /**
     * Reads a line of text.  A line is considered to be terminated by any one
     * of a line feed ('\n'), a carriage return ('\r'), or a carriage return
     * followed immediately by a linefeed.
     *
     * @return A String containing the contents of the line, not including
     * any line-termination characters, or null if the end of the
     * stream has been reached
     * @throws IOException If an I/O error occurs
     * @see java.nio.file.Files#readAllLines
     */
    public String readLine() throws IOException {
        return readLine(false);
    }

    /**
     * Skips characters.
     *
     * @param n The number of characters to skip
     * @return The number of characters actually skipped
     * @throws IllegalArgumentException If <code>n</code> is negative.
     * @throws IOException              If an I/O error occurs
     */
    public long skip(long n) throws IOException {
        if (n < 0L) {
            throw new IllegalArgumentException("skip value is negative");
        }
        synchronized (lock) {
            ensureOpen();
            long r = n;
            while (r > 0) {
                if (nextChar >= nChars)
                    fill();
                if (nextChar >= nChars) /* EOF */
                    break;
                if (skipLF) {
                    skipLF = false;
                    if (cb[nextChar] == split) {
                        nextChar++;
                    }
                }
                long d = nChars - nextChar;
                if (r <= d) {
                    nextChar += r;
                    r = 0;
                    break;
                } else {
                    r -= d;
                    nextChar = nChars;
                }
            }
            return n - r;
        }
    }

    /**
     * Tells whether this stream is ready to be read.  A buffered character
     * stream is ready if the buffer is not empty, or if the underlying
     * character stream is ready.
     *
     * @throws IOException If an I/O error occurs
     */
    public boolean ready() throws IOException {
        synchronized (lock) {
            ensureOpen();

            /*
             * If newline needs to be skipped and the next char to be read
             * is a newline character, then just skip it right away.
             */
            if (skipLF) {
                /* Note that in.ready() will return true if and only if the next
                 * read on the stream will not block.
                 */
                if (nextChar >= nChars && in.ready()) {
                    fill();
                }
                if (nextChar < nChars) {
                    if (cb[nextChar] == split)
                        nextChar++;
                    skipLF = false;
                }
            }
            return (nextChar < nChars) || in.ready();
        }
    }

    /**
     * Tells whether this stream supports the mark() operation, which it does.
     */
    public boolean markSupported() {
        return true;
    }

    /**
     * Marks the present position in the stream.  Subsequent calls to reset()
     * will attempt to reposition the stream to this point.
     *
     * @param readAheadLimit Limit on the number of characters that may be
     *                       read while still preserving the mark. An attempt
     *                       to reset the stream after reading characters
     *                       up to this limit or beyond may fail.
     *                       A limit value larger than the size of the input
     *                       buffer will cause a new buffer to be allocated
     *                       whose size is no smaller than limit.
     *                       Therefore large values should be used with care.
     * @throws IllegalArgumentException If {@code readAheadLimit < 0}
     * @throws IOException              If an I/O error occurs
     */
    public void mark(int readAheadLimit) throws IOException {
        if (readAheadLimit < 0) {
            throw new IllegalArgumentException("Read-ahead limit < 0");
        }
        synchronized (lock) {
            ensureOpen();
            this.readAheadLimit = readAheadLimit;
            markedChar = nextChar;
            markedSkipLF = skipLF;
        }
    }

    /**
     * Resets the stream to the most recent mark.
     *
     * @throws IOException If the stream has never been marked,
     *                     or if the mark has been invalidated
     */
    public void reset() throws IOException {
        synchronized (lock) {
            ensureOpen();
            if (markedChar < 0)
                throw new IOException((markedChar == INVALIDATED)
                        ? "Mark invalid"
                        : "Stream not marked");
            nextChar = markedChar;
            skipLF = markedSkipLF;
        }
    }

    public void close() throws IOException {
        synchronized (lock) {
            if (in == null)
                return;
            try {
                in.close();
            } finally {
                in = null;
                cb = null;
            }
        }
    }

    /**
     * Returns a {@code Stream}, the elements of which are lines read from
     * this {@code BufferedReader}.  The {@link Stream} is lazily populated,
     * i.e., read only occurs during the
     * <a href="../util/stream/package-summary.html#StreamOps">terminal
     * stream operation</a>.
     *
     * <p> The reader must not be operated on during the execution of the
     * terminal stream operation. Otherwise, the result of the terminal stream
     * operation is undefined.
     *
     * <p> After execution of the terminal stream operation there are no
     * guarantees that the reader will be at a specific position from which to
     * read the next character or line.
     *
     * <p> If an {@link IOException} is thrown when accessing the underlying
     * {@code BufferedReader}, it is wrapped in an {@link
     * UncheckedIOException} which will be thrown from the {@code Stream}
     * method that caused the read to take place. This method will return a
     * Stream if invoked on a BufferedReader that is closed. Any operation on
     * that stream that requires reading from the BufferedReader after it is
     * closed, will cause an UncheckedIOException to be thrown.
     *
     * @return a {@code Stream<String>} providing the lines of text
     * described by this {@code BufferedReader}
     * @since 1.8
     */
    public Stream<String> lines() {
        Iterator<String> iter = new Iterator<String>() {
            String nextLine = null;

            @Override
            public boolean hasNext() {
                if (nextLine != null) {
                    return true;
                } else {
                    try {
                        nextLine = readLine();
                        return (nextLine != null);
                    } catch (IOException e) {
                        throw new UncheckedIOException(e);
                    }
                }
            }

            @Override
            public String next() {
                if (nextLine != null || hasNext()) {
                    String line = nextLine;
                    nextLine = null;
                    return line;
                } else {
                    throw new NoSuchElementException();
                }
            }
        };
        return StreamSupport.stream(Spliterators.spliteratorUnknownSize(
                iter, Spliterator.ORDERED | Spliterator.NONNULL), false);
    }
}
